Brain requires large quantity of energy to maintain its internal environment and its activity so that the brain needs a constant supply of glucose and oxygen for its normal metabolism. The impaired cerebral energy metabolism due to the decreased blood flow inhibits brain activity, whereby inhibits the function of a corresponding organ controlled by the damaged area of the brain. Such an abnormality in physical condition or bodily function associated with partial and sudden brain disorder is essential to cerebrovascular disorder (cerebral stroke). Cerebrovascular disorder is classified as “cerebral infarction” wherein ischemic necrosis is caused in the perfused area in the brain tissue by blockage of blood flow due to the occlusion of the artery of the brain; “cerebral hemorrhage” caused by the rupture of a blood vessel in the brain, and “transient cerebral ischemic attack” wherein observed the temporal diminution of brain blood flow with rapid restoration thereof. Moreover, “cerebral infarction” can generally be classified into two major categories such as cerebral thrombosis and cerebral embolism by its causations.
Cerebrovascular disease was the first leading cause of death until replaced by cancer in 1981 since tuberculosis had been brought under control; and now is the third leading cause of death which in turn was replaced by cardiac disease in 1985. Cerebrovascular disease was the third leading cause of death in Japan in the (fiscal) year of 1999 with the rate of 110.8 deaths/100,000 population (the Ministry of Health, Labor and Welfare statistics in the year of 1999.) And, the rate of death from cerebral infarction was reported as 57.7 per 100,000 population. However, it is noted that the patients suffering from cerebral infarction including chronic phase has significantly been increased in number compared to those who are suffering from cancer and cardiac disease associating with the increased longevity. Although majority of nonfatal cerebral infarctions have relatively small lesions, they have come to attract people's attention in consequence of the aging of population as high incidence of cerebellar infarctions results in multiple infarct dementias (cerebrovascular dementia). Therefore, not only the development of the treatment but also the establishment of prophylactic strategy and the manufacture of prophylactics against the cerebrovascular diseases are desired. Nevertheless, potent prophylactics have not been developed yet.
Starting with X-ray computed tomography developed in 1970s, the development of various medical imaging technologies for diagnosis enabled the early detection of the celebrovascular diseases and contributed to the progress in revealing the pathophysiology thereof. Cerebroprotective agents, anti-platelet agents, antithrombin agents, etc. have been employed in the treatment of cerebral infarction, however, the therapeutic effects thereof are not sufficient enough, thus the more effective treatment is desired.
PAR-2 is a member of protease-activated receptors family, and PAR-1, PAR-2, PAR-3 and PAR-4 in PAR family have currently been cloned. PAR families are G protein-coupled receptors with seven-transmembrane domains, but its activation mechanism is significantly different from that of other seven transmembrane G proteins-coupled receptors. Particularly, proteases cleave at specific sites of amino-terminus within PAR molecule i.e. a receptor; a newly exposed terminus serves as tethered ligand, folding back onto the receptor, and thereby activating it (Physiol. Rev., 2003; 84:579-621; Pharmacol. Rev., 2001; 53:245-282). While PAR-1, PAR-3 and PAR-4 are activated by thrombin, PAR-2 is not activated by thrombin but activated by trypsin or tryptase.
PAR-2 was cloned by Nystedt et al. in 1994 (Proc. Natl. Acad. Sci. USA, 1994; 91:9208-9212). Unlike the other PAR families, PAR-2, as mentioned above, is activated by the different proteases such as trypsin or tryptase. Other PAR-2 activators are synthetic peptides having the same amino acid sequences as aforementioned tethered ligand, the derivatives thereof trans-cinnamoyl-LIGRL-NH2, trypsins, tryptases, tissue factors/factor VIIa, factor Xa, acrosin which is a sperm proteases, tryptic serine proteases identified from the brain of a rat (Physiol. Rev., 2003; 84,579-612; Pharmacol. Rev., 2001; 53,245-282).
PAR families are widely expressed in many organs and tissues in vivo, and involvement of PAR activations in physiological significances and pathological conditions has been investigated in various cells, tissues, and animal models. Exertion of versatile physiological functions of PARs in vivo has been revealed as 1) control of blood coagulation and activation of vascular endothelial cells, 2) control of contraction and relaxation of the gastrointestinal tract, as well as secretion of saliva or digestive juice, 3) control of contraction and relaxation of respiratory tract, as well as secretion of cytokines or proteases from the bronchial epithelial cells, 4) control of inflammation reaction, and 5) control of survival of the central neuronal cells, edema and nociception (Physiol. Rev., 2003; 84:579-621; Pharmacol. Rev., 2001; 53:245-282).
In addition to the above-mentioned functions, it is reported in the in vitro and in vivo experimental systems that PAR-2 causes leukocyte rolling and adhesion; neutrophil infiltration; secretion of inflammatory cytokines and leakage of plasma proteins; as well as onset and exacerbation of arterial sclerosis, skin inflammation, arthritis and acute inflammation (Physiol. Rev., 2003; 84:579-621; Parmacol. Rev., 2001; 53:245-282).
PAR-2s, expressed in various cells in the brain, are believed to be one of the factors that exacerbates pathological conditions associate with nerve cell apoptosis in the brain because the experimental systems with cultured nerve cell demonstrated the dose-dependent cell death induced by addition of PAR-2 activating peptides to the cell culture (J. Neurochem., 1997; 69:1890-1896); and the correlation between nerve cell death under hypoxic condition and increased expression of PAR-2 (Eur. J. Neurosci., 2001; 14:595-608). However, the relationship between PAR-2 and cerebral infarction is still unrevealed.